MIPS: MSP71xx: Resolve multiple definition of plat_timer_setup

There have been a number of compile problems with the msp71xx configuration
ever since it was included in the linux-mips.org repository.  This patch
resolves the "multiple definition of plat_timer_setup" problem, and creates
the required get_c0_compare_int function.

This patch has been compile-tested against the current HEAD.

Signed-off-by: Shane McDonald <mcdonald.shane@gmail.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>